The present invention relates to a magnetic head for a magnetic recording-reproducing apparatus such as a VTR and, in particular, to a construction of multichannel multiple heads.
With the advancement of image quality and increasing functions of the VTR, there have been attempts to provide a number of heads cooperable with the magnetic recording. Multichannel heads, in which a number of chips are carried on one head base are highly desirable from the point of view of the spacing of the rotating cylinder for carrying the head, the cost of the head assembly, system requirements, and so on.
In FIGS. 5a and 5b, a conventional double azimuth head is provided for a VTR for home use. In this head, two head chips 1a and 1b are carried in proximity to each other on a head base 2 so that multiple functions can be obtained. However, such heads, for example, heads for the same purpose, recording-reproducing heads, only recording heads, or only reproducing heads are used in multiple forms and disposed on the same chip. In such heads, in order to improve the tape contact of two heads, the center of curvature R of the head tip is offset by a distance d with respect to a perpendicular line from the head gap as shown in FIG. 5b. In the abovementioned heads, since the right and left heads are in close proximity to each other at an interval of at most several hundreds .mu.m, it has been determined that a proper tape contact can be obtained only by forming the curvature R, and such heads have now been mass produced.
On the other hand, in multichannel heads which are used in more sophisticated VTRs for broadcast or for home use, the distance between the adjoining heads is, in some cases, over 1 mm. In FIGS. 6a and 6b, a conventional triple-channel head is shown for explanation purposes and, as a practical matter, heads having two and six channels have been used.
To manufacture a triple channel head, the head chips 1a, 1b and 1c of FIG. 7a are respectively ground to aspherical surface shapes as shown in FIG. 7b. In this case, the center of curvature R of each head tip is respectively offset with respect to the perpendicular line from each gap 3a, 3b and 3c by a distance d corresponding to the position where each head chip is affixed to the head base 2. Then, the head chips 1a, 1b, and 1c are affixed to the head base 2 and parallel to each other as shown in FIG. 7c. Finally, in order to cause the center of protrusion of each head chip to approximately coincide with each gap position thereby ensuring a sufficient initial contact when the head is mounted on the rotating drum, the head is lapped with a lapping tape, etc. so as to form the final shape shown in FIG. 7d.
FIGS. 6a and 6b show the above mentioned head and its sliding surfaces after the head has been mounted on the actual device so as to enable the head to slide with respect to the tape. As shown in FIG. 6b, the head chip 1a is the chip which first contacts the tape. A number of problems arise in the manufacturing of the head by the above-mentioned method.
More particularly, since the space between the head chips is over 1 mm, some portions of the surface of each head chip are not lapped (FIG. 6a) due to the shape of each head chip; therefore, the sliding surface has discontinuities at portions which are not lapped. Since the tape contact mark arrives at each discontinuity, dust is trapped at each of these portions. In particular, a significant quantity of dust is trapped at the head chip 1a positioned at the protruding side.
Furthermore, since the gap is not positioned at the center of the tape contact mark (FIG. 6a), insufficient tape contact results. Further, the tape contact varies after extended running of the tape. Since the perpendicular line from each gap does not coincide with the center of the rotating drum, the space of each gap changes, in particular, in the head chips 1a and 1c, after extended running of the tape.
Additionally, upon a recording on a tape which has once been recorded, the former recording is not completely erased if the dust is trapped in the recording head.
As shown in FIG. 8a, after extended running, a large quantity of dust is trapped in the unlapped portions and, more particularly, at a back of the gap of the leading head chip. If dust is trapped at this position, problems arise such as, for example, clogging of the head, reduction of the gap, etc. By virtue of such problems, the recording head sometimes does not record important information which is a significant problem in business use of the recording apparatus.